Yemen's population needs 4.2 billion dollars in aid this year as the world's biggest humanitarian crisis has deteriorated over the past 12 months of war, UN Secretary General Antonio Guterres told donor countries in Geneva on Tuesday.

The Houthi forces have agreed to draw back from two Yemeni ports on Monday while withdrawal from the main Hodeidah port will occur later alongside a retreat by coalition-backed forces massed outside the city, UN and Yemeni sources said.